The aim of the present research is to assess attention capture, sustained attention, and defensive reflex engagement during emotional perception in anxiety patients diagnosed with and without co-morbid major depression, and in healthy control participants. Previous studies suggest that anxious, depressed, and control participants differ variously in affective processing: 1) in early and later stages of processing, 2) in response to intact or degraded affective cues, and 3) and in the modulation of attentional (e.g., RT) or emotional (e.g., startle blink) indices. Whereas fearful, anxious patients generally show rapid attention capture and strong emotional engagement in response to threat cues, relative to controls, results for depressed patients are mixed. Here, we use a multi-modal measurement array (brain, reflex, and reaction time) to address attentional and emotional engagement in socially anxious patients -- both depressed and non-depressed -- as these processes develop chronometrically during picture perception. The overall hypothesis is that whereas fearful anxiety is characterized by robust activation of the brain's defense system, quickly attracting attentional resources and mobilizing the organism to confront even half-perceived threats;comorbid depression represents a more chronic stage in the development of affective pathology in which attention and emotion are uncoupled, possibly reflecting top down effects of perseverative rumination that delays or diverts external focus, or indicative of a general systemic disorder, based on a history of chronic stress, that blunts defensive reflexes and coping actions. To assess potential differences in a single paradigm, the temporal development of attention and emotion are assessed using an acoustic probe methodology that efficiently assesses these processes when participants view affective cues: (1) The blink reflex to a startling acoustic probe is a robust measure of the degree to which the brain's defensive system is engaged;(2) the P3 component of the event-related potential (ERP) to an acoustic probe provides a direct, brain-based measure of sustained attention allocation;and (3) reaction time (RT) to an acoustic probe reflects early attention capture. Because acoustic probes are easily presented at various temporal delays after picture onset, the probe methodology opens a chronometric window on the developing trajectories of both attention to threatening cues and emotional reactivity. PUBLIC HEALTH RELEVANCE: Heightened attention and emotion to aversive events is often described as underlying the persistence of anxiety and depression in patients diagnosed with these disorders. The proposed research explores the time course of attention capture and emotional engagement when socially anxious patients diagnosed with or without comorbid depression are confronted with threatening cues. A variety of existing hypotheses regarding differences and deficits in anxiety and depression are assessed in a single psychophysiological session that could help to address perplexing patterns found in past studies as well as to illuminate basic mechanisms in co-morbid pathology that are fundamental for developing new assessment and/or therapeutic techniques.